ST. LOUIS — Disaster, in a playoff race, is relative. The St. Louis Cardinals hammered the Washington Nationals so early and so thoroughly Friday night that the visitors pulled half their team off the field by the fifth inning. Edwin Jackson recorded four outs, two of them on a double play by the opposing pitcher and one on a sacrifice fly to the warning track. They made an utter hash out of Game 157.

Each night brings the Nationals a new lesson about meaningful September baseball, and they learned Friday about solace. After the 12-2 thumping they absorbed, the Nationals will report back to Busch Stadium on Saturday with champagne chilling on ice somewhere near, just in case.

“This is what it’s all about,” Manager Davey Johnson said before the game. “It’s a whole new, different feeling when you’re playing for a pennant or in the postseason. Every game, every pitch means something. Experience does help, but going through it helps, too.”

Against the team with which he won the 2011 World Series, Jackson never gave the Nationals a chance. The Cardinals scored five runs off him in the first and then four more before he could record the second out of the second inning. He allowed nine runs, eight earned, on seven hits and four walks. He fell behind eight of the 15 batters he faced. Of his 202 prior starts, one had been shorter. In 56 pitches, he delivered more wild pitches (two) than balls the Cardinals swung at and missed (one).

“It’s very disappointing and embarrassing,” Jackson said. “Your club is in a pennant race, and you have a game like that. It definitely leaves a bitter taste in your mouth that you did absolutely nothing to give your team a chance to win.”

The Nationals could open the playoffs against the Cardinals, and if they do, Friday night may serve as an argument for them to slot left-hander Ross Detwiler ahead of Jackson in the playoff rotation. In his first start this year against the Cardinals, on Aug. 30, Jackson allowed no earned runs in eight dominant innings. Last night, they splattered him. Still, Johnson said the outing would not affect his judgment of Jackson’s place.

“I just throw it out,” Johnson said.

Jackson took the mound with a one-run lead, given to him when Adam LaRoche scored Bryce Harper with a two-out single for his 99th RBI. Before Jackson could record his first out, the Nationals trailed, 3-1.

The meltdown could not have been predicted. In his last start, Jackson went eight innings and allowed just one run against the Brewers. Johnson gave him six days of rest as he re-jiggered his rotation so three left-handers would face the Phillies.

But Jackson’s blowup was instant and complete. He issued two walks in the first inning, including one to Carlos Beltran with the bases loaded. He ended the inning with a double play ball from Adam Wainwright, but it offered only momentary reprieve. Jon Jay led off the second with a double to left-center field gap. Yadier Molina delivered the final blow, a two-run homer to left.

“It was lack of rhythm, it was lack of everything,” Jackson said. “It felt just like it looked.”

For the cherry on top, Jackson walked the last batter he faced. As Johnson trudged out to come take the ball from him, the Nationals trailed, 9-1, and they had started to forget about the game.

“That’s what I told Edwin when he left,” LaRoche said. “I said, ‘Go inside and totally forget about this one. Act like it didn’t happen.’ That was a beating. . . . I told Edwin, ‘Just chalk this up to bad luck. We need you in five days.’ ”

In the fifth inning, Johnson made a line change. Mark DeRosa, Roger Bernadina, Corey Brown and Jesus Flores replaced Ryan Zimmerman, Harper, Jayson Werth and Kurt Suzuki. An inning later, Ian Desmond and LaRoche came off for Steve Lombardozzi and Chad Tracy.

Their only hope flickered back east, in Atlanta. The Braves took a 1-0 lead into the seventh inning, and it appeared the Nationals’ lead could shrink to three games and the final weekend of the season could be a dogfight. And then Mets outfielder Lucas Duda launched a three-run homer, enough for the Mets to hang on and snap Atlanta’s five-game win streak. If Duda finds a new watch at his locker Saturday, he will know from where it came.

“Go Mets,” Werth said.

In their other race, the one Johnson professes not to care about, Homer Bailey threw a no-hitter for the Cincinnati Reds, the team Washington is jostling with for the best record in the NL. The Nationals and Reds share the same record, but the Nationals, by virtue of their 5-2 edge in the season series, only have to tie with Cincinnati to ensure the top seed in the National League.

Johnson hoped the Braves would lose, of course, but he could think of one benefit of them keeping the pressure on. The Nationals have few players with any playoff experience, but Johnson believes a gantlet in September can prepare them for October.

“I like these games all meaning something,” Johnson said. “I think it’s a good education.”

Friday, they learned the kind of weird sensations a pennant chase can bring. At any other point in the season, a loss like Friday’s would raise concerns and overturn clubhouse tables. Now, the out-of-town scoreboard can provide rescue. The worst of games can bring you a step closer to a division title. The days you want to forget can push you to the brink of a moment you will always remember.